state of current knowledge regarding tyre braking …...state of current knowledge regarding tyre...

State of current knowledge regarding tyre braking performance of modern aircraft tyres on flooded runways Gerard van Es, NLR, Paris, 31st March / 1st April 2016

SAFETY | FUTURE SKY

DGAC-STAC Symposium Runway Surface Conditions Assessment and Reporting

Background q  European Action Plan Prevention of Runway Excursions

provides recommendations to reduce runway excursions in Europe;

q  Action Plan identified areas were research is needed to further reduce runway excursion risk, like:

q  Braking performance of modern aircraft on flooded runways.

q  Future Sky Safety Project addresses this topic amongst others:

q  Presentation will discuss current state of knowledge.

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Definitions What is a flooded runway?

q  Legal: A runway can be considered flooded when more than 25 percent of the runway surface area is covered by water that is more than 3 mm in depth;

q  Alternative: A runway on which the water depth exceeds the ability of tyre tread and runway texture to prevent water film build-up below the tyre:

q  Could be more or less than just 3 mm of water.

SAFETY | FUTURE SKY 3

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Flooded runway

Wet runway

VERSUS

Braking friction-Dry, Wet, and Flooded

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Factors influencing friction on flooded runways q  Runway texture (macro- and microtexture, runway

grooves); q  Ground speed; q  Tyre inflation pressure; q  Tyre tread depth (dynamic hydroplaning); q  Tyre type (bias-ply, radial, H-type):

q  Impact on dynamic hydroplaning.

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Comparison of full dynamic hydroplaning speeds different tyre designs

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160

140

120

100

80

60

40

20

0

Hyd

ropl

anin

g sp

eed

(kt)

250200150100500Tire pressure (psi)

bias ply (new designs 1975-onwards) radial belted H-type bias ply (old designs 1960s)

9√p

6√p

Empirical equations for dynamic hydroplaning speed q  Rotating wheel :

o  Classical NASA ≈9.0√p o  Modern bias-ply tyres ≈8.0√p o  H-type tyres ≈7.5√p o  Radial tyres ≈6.9√p

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q  For spin-up dynamic hydroplane speed reduces by 15%;

q  Note: dynamic hydroplaning speed also influenced by: water depth, macro texture, tyre grooves, and tyre footprint.

Review of experimental data on braking capabilities of aircraft tyres on flooded runways q  Most data were from period 1959-1989;

q  Data from full-scale aircraft tests as well full-scale traction facilities were collected;

q  No friction data found for radial and H-type aircraft tyres (only for wet runways).

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Example of data sources

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NASA full-scale traction facility FAA CV-880 flight tests

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Full-scale aircraft data Flooded runways

Models for braking friction on flooded runways

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Final Remarks q  Study summarises the state of current knowledge

regarding tyre braking performance of aircraft tyres on flooded runways:

q  Full report available from the FSS website.

q  Very limited data on flooded runway braking of aircraft with modern tyres and modern anti-skid systems:

q  Flight tests in FSS project should partly fill this gap.

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Aircraft to be tested in FSS project

http://www.futuresky.eu/projects/safety